confused, as the cars I've had had a coolant tank with a "fill to this line hot" and it was about 2/3rds full at that line,

And my 71 c-10 doesn't have anything, just a hose running down the side of the rad. And I want to build a tank, would it be like the 80's cars with it 2/3rd filled or empty like you are say'n until a boil over and then sucked back in afterwards basicly always being empty providing the hose in the overfollow you listed hose collected every drop when it was being sucked back in..

Sorry, I was thinking of a minimum 16 oz. overflow vessel like used in drag racing, not a coolant recovery system.